Internal-combustion engines, such as engines that employ the familiar Otto or Diesel cycles, are used widely and commonly in vehicles intended for carrying both persons and goods, such as passenger, transport and goods vehicles, including lorries and locomotives. To summarize, these engines use a fuel with a high content of hydrocarbons, such as fossil fuels or fuels derived from renewable sources, for converting the thermal energy from burning the fuel into kinetic energy.
Today there is increasing concern for reducing emissions produced by internal-combustion engines, which are responsible for a high proportion of the production of CO2 in the atmosphere. Climate change is one of the most important environmental challenges of the present time, possibly with grave consequences. This problem is being caused by intensification of the greenhouse effect, which in its turn is related to the increase in the concentration of greenhouse gases, including carbon dioxide, in the atmosphere.
In recent years, in order to minimize the emission of gases that are harmful to the environment, such as carbon monoxide (CO), hydrocarbon gases (HC), oxides of nitrogen (NOx), as well as of particulates and/or greenhouse gases, a series of technologies has been incorporated in internal-combustion engines. The reduction in gas emissions is related, among other factors, with increase in thermal efficiency of the engine and, consequently, reduction in specific fuel consumption.
In this connection, technologies such as electronic injection, catalytic converters, and particulate filters are nowadays quite widespread and their use is almost obligatory in all internal-combustion engines. Other more recent technologies, such as direct fuel injection, common-rail technology for engines that use the Diesel cycle, and the larger-scale use of technologies that have long been known, such as mechanical compressors or turbocompressors, are also being combined with the aim of increasing energy efficiency and for meeting ever stricter emissions standards.
As a consequence, combustion engines are developing greater power per volume of piston displacement in the cylinder, usually called specific power. The efficiency of a combustion engine in the Otto cycle in the 1980s reached on average 50 HP/L, and today it may easily reach more than 100 HP/L. This means that the combustion pressure within the cylinders has increased considerably, which also means that combustion engines are operating under greater mechanical stresses, higher rotary speeds, and higher temperature. Accordingly, their components must likewise be designed for withstanding these harsher operating conditions, both to guarantee reliability of the unit and maintain its expected useful life, today estimated at about 300000 km for petrol engines of saloon cars.
In addition, there is increasing adoption of technology usually known as Start/Stop, in which the combustion engine is turned off automatically when the vehicle is not moving, and is turned on again when the driver operates the clutch or releases the brake pedal, for example. The aim of this technology is to reduce fuel consumption and consequently reduce the emission of gases when the vehicle is not in motion, for example when stopped at traffic lights or in traffic.
However, constant stopping and restarting of a combustion engine means that components are submitted to reduced lubrication more frequently, thus increasing the wear of its components.
Therefore internal-combustion engines are increasingly being subjected to harsher operating conditions, both in the sense of increases in mechanical stresses, rotary speeds and temperature, and in the sense of reduced lubrication.
In parallel, there are efforts to reduce the weight of the components of the engine and the costs associated with manufacture, relationships that must be considered when choosing the materials that will be used in its construction. Accordingly, materials technology is also an important area of development for internal-combustion engines.
One of the components that is more affected by the stresses generated by combustion engines is the connecting rod, which provides the connection between the piston and the crankshaft to transform the linear motion of the piston into rotary motion. The connecting rod is joined at one end to the piston, and at the other end it is joined to the crankshaft. In the present specification, the end of the connecting rod that is joined to the piston is called the small end, and the end of the connecting rod that is joined to the crankshaft is called the big end.
At the big end, between the connecting rod and the crankshaft, a bearing is used, made of a material of lower hardness, in order to reduce the friction between these two components. At the small end of the connecting rod, a bearing is also used, mounted between the small end and the gudgeon pin, also with the aim of reducing the friction between the components. The bearings used in the connecting rods also have the function of allowing easy assembly, compensating misalignments of assembly and accommodating particles, as is well known by a person skilled in the art. Although the example mentioned here refers to bearings mounted in connecting rods, it is certain that bearings may be used in other components of a combustion engine, such as the bearings of the crankshaft and of the camshaft etc., or in any other mechanical component that uses a bearing or requires bearings or bushes.
The bearings for applications in internal-combustion engines generally consist of a carbon steel cap coated internally with an alloy based on Pb and Sn (known as Babbitt metal or White Metal), or an alloy based on Al combined with Sn in varying concentrations, or else a copper alloy containing varying concentrations of Pb.
However, as mentioned above, the operating conditions of internal-combustion engines are becoming harsher and harsher, and bearings made of alloys based on Pb and Sn, as well as those based on Al, fail through fatigue and do not guarantee the necessary reliability and durability. In addition, there are restrictions on the use of lead as an alloying element, as it is highly toxic.
The present invention aims to overcome these drawbacks, among others.